1. Field of the Invention
The invention relates to ink recording devices and, more particularly, to a pivotable ink shield for the writing head which is pivotably movable to shield, wipe, and permit flushing of writing head dispensing openings.
2. The Prior Art
In the case of typical ink recording devices, a writing head is moved in line-by-line fashion along a recording medium on a driven writing head carrier. The writing head can, in some presently used embodiments, be an ink mosaic writing head in which piezoelectrically operated writing jets or dispensing openings are arranged in a mosaic pattern. The writing jets are supplied with writing liquid or ink from an ink supply and the individual jets are controllably actuated by a character generator. The jets of the writing head are formed by somewhat cylindrical bores which are surrounded by piezoelectric drive elements. The operating open ends of the bores are located at an end face of the writing head and a nozzle plate may be provided on the end face.
In normal practice, writing heads of the above-described type are positioned in close space relationship to the recording medium, which may be a roll of paper. Due to this close positioning dirt will oftentimes become lodged against the nozzle plate with attendant adverse operating results. Such dirt contamination of the nozzle plate is frequently encountered during paper change or change to other recording medium carriers as may be used in the particular construction. Since the piezoelectrically operated writing jets are constantly filled with ink, the danger also exists that, during changing of the recording medium, the recording medium will be pulled passed the jet openings of the writing head and thereby sprayed or smeared with ink.
The German AS No. 2702663 discloses an arrangement whereby plastic plug members are used to close the jets of a writing head during periods of non-printing. The plug members are moved via a drive device between a rest position wherein the plug members cover the bore exits of the writing head with an elastic covering plate and an operating position wherein the plug members are positioned away from the writing head. One drawback with this arrangement, however, is that the plug members are fixedly positioned on the writing device so that the writing head must be brought to a specific position for the plug members to cover the jet openings.
U.S. Pat. No. 4,112,435 discloses a screen or plate member for protecting and cleaning the jet outlet openings of an ink mosaic writing head. The screen is pivotable against a spring force via an electromagnet drive means between a blocking position along the jet outlets and an operating position away from the jet outlet openings. A resilient wiper element, fastened to the screen, sweeps over the jet outlet openings during movement of the screen from the blocking to the operating positions. The electromagnet drive means engages with a lever arm connected to the screen for movement of the screen between its two positions.
The German OS No. 2742963 discloses an electric motor drive linkage arrangement for pivoting an ink shield between a blocking position when the writing head is not to be used and an operating position whenever the writing head is to be used. The ink shield is formed with a window opening which is positioned in front of the jet outlet openings of the writing head in the operating position and is fastened directly onto the writing head.
These above-mentioned prior art devices are each of relatively complicated construction not readily practical for protecting and cleaning ink dispensing openings of a writing head. The problem is to provide for an ink shield and associated drive mechanism which makes it possible to automatically close writing head outlet openings during rather long pauses between printing operations and to effectively clean the plurality of ink dispensing openings. A very effective way in which ink dispensing openings may be cleaned is to provide for periodic flushing of the outlet openings. The present invention provides for a simple constructional arrangement whereby writing head dispensing openings may be shielded, wiped, and permitted to flush during pauses in printing operation.